Super-adhesives: gecko + mussel = geckel

In the latest attempt to improve on natural adhesives, scientists mix …

A short time back, we covered how materials scientists were attempting to more accurately mimic the behavior of the small hairs on the feet of geckos in designing reusable adhesives. A writeup of the latest attempt along these lines is being published in Nature today, and it takes the work off in a new and intriguing direction: mixing gecko-inspired designs with what we know about other robust natural adhesives.

In this paper, as suggested by the image at right, the other adhesive is derived from mussels, shellfish that generate some extremely sticky structures that keep them attached to rocks and other structures. That adhesive has to work well under water, and be robust enough to handle the pounding of waves. Previous work had identified the active ingredient in mussel adhesion as being a modified form of the amino acid tyrosine called DOPA. The chemical structure of DOPA allows it to form a variety of reversible bonds with surfaces, some significantly stronger than the van der Waals forces that geckos rely on. Measurements had shown that DOPA's interactions with a metal oxide surface was the strongest ever detected for a small molecule.

The paper describes the combination of the physical structure of gecko adhesive with the chemical properties of mussel adhesive to create something the authors term "geckel." Geckel is composed of a repeating array of small fibers, 400 nm across by 600 nm high. Once manufactured, these fibers are given a chemical coating with a polymer that is composed of about 17 percent DOPA by weight. Applying the coating was as simple as dipping the gecko-style fibers in a solution of the polymer.

The results were impressive. Under dry conditions, geckel stuck to surfaces well enough that three times the force was needed to dislodge it compared to the uncoated fibers. In water, the improvement was over 14-fold; geckel in water stayed stuck much better than the uncoated fibers did under dry conditions. The coating was also extremely durable, as the material retained 85 percent of its strength even after 1,100 adhesion/detachment cycles.

We may not be seeing geckel on the store shelves immediately, but the manufacturing technique seems straightforward enough that it may not take as long to appear as many of the other discoveries we report on. And, as a biologist, it's great to see that materials scientists think that when a little biology (geckos) is good, more biology (geckos + mussels) can be even better.